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Weather and time rotation would be awesome, personally I always love spooky nighttime atmospheres.
Also to add some flavour to previous comments we've made, just because something wasn't done at the time because of performance issues, doesn't mean it's off the table forever.
A prime example of this (for any of you who have been around long enough) is destructible trees. This was work that was pushed off for a very long time due to the performance cost until we got to a spot where we (and the supporting tech) could do it without a massive hit :)